STUD 3K1865 - Caterpillar

System Operation Description:The speed sensor is a passive magnetic speed sensor. The sensor indicates the engine speed and the crankshaft position to the Timing Control Module (TCM).The sensor outputs a sinusoidal waveform. The signal is created when the teeth on the flywheel pass beneath the speed sensor pickup. The frequency of the signal is proportional to the engine speed.
Illustration 1 g00664421
Illustration 2 g00664423
Refer to the engine wiring diagram for the configuration of the wiring.The TCM monitors the characteristic resistance of the sensor in order to diagnose open circuits and short circuits.Test Step 1. Check for Connector Damage.
Remove the power from the timing control system.
Check the connectors and wiring for the following problems: damage, corrosion, abrasion and incorrect attachment. Refer to Troubleshooting, "Inspecting Electrical Connectors".Expected Result:The connectors and wiring are free of the following problems: damage, corrosion, abrasion and incorrect attachment.Results:
OK - The connectors and wiring are in good condition. Proceed to test step 2.
Not OK - The connectors and/or wiring require service.Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Reconnect all of the connectors. Stop.Test Step 2. Check the Resistance of the Sensor.
Disconnect the speed sensor from the engine harness.
Use the 4000 ohm scale to measure the resistance between pin A and pin B at the sensor connector.Note: Be sure that you measure the resistance at the sensor connector. Do not measure the resistance at the harness connector.Expected Result:The resistance is between 100 and 600 ohms.Results:
OK - The sensor is OK. Proceed to test step 3.
Not OK - The sensor is faulty.Repair: Replace the sensor. Reconnect all of the connectors. Stop.Test Step 3. Check the Engine Harness.
Connect the speed sensor to the engine harness.
Disconnect the TCM from the engine harness.
Measure the resistance at the connector for the TCM. Use the 4000 ohm scale to measure the resistance between pin T and pin N.Expected Result:The resistance is between 100 and 600 Ohms. The value is equal to the reading from test step 2.Results:
OK - The harness does not have an open circuit. Proceed to test step 4.
Not OK - There is an open circuit in the harness.Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Stop.Test Step 4. Check the Clearance Between the Sensor and the Flywheel.
Disconnect the speed sensor from the engine harness.
Mark the position of the sensor on the flywheel housing.
Loosen the locknut.
Turn the sensor clockwise until the sensor contacts a tooth of the flywheel.Record the number of turns that are required to make contact. The correct number of turns for the proper clearance is approximately one-half to three-fourths of a turn (180 to 270 degrees).
Remove the sensor from the flywheel housing.
Inspect the sensor for damage and metal filings on the magnetic tip.
Install the speed sensor into the flywheel housing.
Turn the sensor clockwise until the sensor contacts a tooth of the flywheel ring gear.
Turn the sensor counterclockwise for approximately one-half to three-fourths of a turn (180 to 270 degrees).Note: Do not allow the sensor to move when you tighten the locknut.
Tighten the